Infrared spectroscopy of pressure-induced metallization in semiconductors

Mid-IR reflectance spectra were measured in ZnSc. ZnTe, and MnO under high pressure utilizing a diamond anvil cell. The spectral analysis based on the Drude model provided the plasma frequency. scattering time of carriers, and high frequency dielectric constant in high-pressure metallic phases of these materials. In ZnSe, a new intermediate phase was observed in a narrow pressure range near 12 GPa between zincblende and B1 phases. Mid-IR absorption spectrum revealed that the intermediate phase is a nan ow gap semiconductor with the indirect gap of about 0.6 cV, while B1 phase is found to be a semimetal. In ZnTe, an anomalous decrease of the Drude edge was oserved as pressure increases above 20 GPa in the distorted B1 phase. An abrupt rise of the Drude edge in MnO found above 90 GPa demonstrates the occurence of an insulator-metal transition. The transition is found to be closely connected with the high spin-low spin transition (magnetic collapse).